1. Field of the Invention
The present invention relates to copper-free wires, and more particularly, to a copper-free wire which is excellent in feedability and arc stability even though the surface thereof is not copper-plated.
2. Description of the Related Art
Development of a welding wire from a conventional welding electrode for shielded metal arc welding has improved welding workability by a great amount. Recently, welding is being increasingly carried out via semi-automatic welding, automatic welding or robot welding since welding wires can be fed by a large amount regardless of places. In particular, the ratio of the semi-automatic welding is increasing even in the shipbuilding industry so that the amount of the welding wires in use is increasing.
As welding conditions are developed and applied into various forms due to welding automation and diversification of applications as above, the basic property of welding wire is a principal factor about feedability besides arc stability.
For the purpose of satisfying quality requirements for a welding wire, conductive metal such as copper is conventionally plated on welding wire surface so as to guarantee properties of the wire such as conductivity, feedability and rust resistance. In other words, conductive metal such as copper is plated on the welding wire surface so as to enhance the conductivity and arc stability in respect to a welding tip (contact tube), reduce the quantity of spatter or fume generation, and ensure an excellent weldability. In a copper-plated wire, however, plating quality is directly associated with the quality of a product wire so that the plating quality becomes the most prominent management factor in the wire quality. That is reason why steel parts beneath a plated layer come out by having poor copper coating, and this phenomenon thereof is directly associated with problems such as conductivity at a contact tip (contact tube), feedability due to friction in a conduit cable and rust resistance of the wire.
Therefore, in the copper-plated wire, efforts for obtaining excellent plating quality have been made in order to improve the quality of the wire.
In the meantime, plating adhesiveness is one of the most common factors for estimating the plating quality as above, and several methods are represented in the JIS H8504 which estimates the plating adhesiveness. One of the easiest methods is a adhesiveness scheme wound like coil shape, by which a wire is wound around itself or a mandrel for at least several times so as to estimate cracking or peeling off of a plated layer on the wire surface and is estimated through magnification with a microscope. In the above estimation scheme, the cracking or peeling off of the plated layer occurs by a smaller amount if the wire has more excellent plating adhesiveness. This property is directly linked to the feedability of the wire.
However, nevertheless several advantages including the above, the copper-plated wires have drawbacks such as difficulties in plating quality management, environmental problems originated from plating processes, poor quality insufficient to desirable level and the like. Lately, it is being required to develop a copper-free wire having qualities at least the same as those of the plated wires. Although technologies have been actively developed for copper-free wires up to now, the copper-free wires have failed to show properties more excellent than those of the copper-plated wires considering feedability or other workability thereby interrupting commercialization thereof. In particular, the copper-free wires require a novel approach different from the conventional plated wires in order to improve the properties relating to causing by non-plating such as conductivity, feedability and rust resistance.
In the meantime, the copper-free wires introduced up to now inevitably adopted a surface treatment agent on the wire surface. Examples of those wires are disclosed in Japanese Patent No. 2682814 entitled xe2x80x9cWire for Arc Weldingxe2x80x9d, Japanese Laid Open Patent Application No. H11-147174 entitled xe2x80x9cNon-Plating Welding Wire for Steelxe2x80x9d, Japanese Laid Open Patent Application No. H12-94178 entitled xe2x80x9cWelding Wire Without Platingxe2x80x9d and the like. According to those documents, a feeding lubricant powder such as MoS2, WS2 and C or a mixture thereof is applied to the wire surface or a feeding lubricant is coated on the wire surface in order to enhance feedability. Further, Japanese Laid Open Patent Application No. H12-117483 entitled xe2x80x9cWelding Wirexe2x80x9d discloses an uneven wire having a uniform wavelength in the circumferential direction of the wire, in which excellent arc start property can be obtained through management of a peak intensity range detected in the power spectra. Also, Japanese Laid Open Patent Application No. H12-317679 entitled xe2x80x9cNon-Plating Wire for Arc Welding and Arc Welding Methodxe2x80x9d discloses a technology for sticking particles of insulating inorganic powder and/or conductive inorganic powder on the welding wire surface with water soluble polymer so as to decrease the quantity of fume or spatter generation.
With the above documents, however, fume is inevitably generated due to fine powder coated on the wire surface. Since uniform coating of powder can be hardly carried out, quantitative management is difficult, and the quantity of spatter generation may be accelerated rather if coated ununiformly.
Further, as disclosed in Korean Patent No. 134857, it is proposed to smoothen the wire surface to the utmost to reduce friction within a conduit liner thereby enhancing feedability.
In the above copper-free wires, however, a wire manufacturing process generally employs a wet skin pass technique in the final stage thereof, in which the rust resistance of the wire is obtained via lubricant pool management, selection of a surface treatment agent and uniform coating.
Further, the above copper-free wires have a poor feeding ability compared to the conventional plated wires in a high speed welding and a long cable condition in which its feedability is heavily influenced by factors such as the smoothness of the wire surface and tensile strength (T/S). The poor feeding ability generates slip in a feeding roller of a feeder section in welding thereby leading to an irregular feeding.
Accordingly the present invention is provided to solve the foregoing problems of the related art and it is an object of the invention to provide a copper-free wire which has a uniform degree of concave roughness () in the surface thereof to obtain excellent feedability and arc stability.
It is another object of the invention to provide a copper-free wire which does not require a lubricant powder coating, which is treated to the surface of the foregoing non-plating wire, thereby reducing the quantity of fume generation in welding.
According to an aspect of the invention to solve the foregoing object, it is provided a copper-free wire having worked faces meaning faces drawn with dies and unworked faces continued in the circumferential direction on a wire surface, the copper-free wire having LD/LT ranging from 0.51 to 0.84 and LY ranging from 10 to 40 xcexcm when measurement lines are drawn at every 5 xcexcm in a width direction of a measurement area (10,000 xcexcm2=100 xcexcmxc3x97100 xcexcm) on the wire surface about 4 wire faces, in which each of the measurement straight lines having a length in the circumferential direction includes at least two worked faces and unworked faces, respectively, in the measurement area, and its starting point and termination point which are all positioned on contact points of the worked faces and the unworked faces, wherein the LD/LT is defined according to Equation 1, and the LY is defined according to Equation 2:                                                         LD              /              LT                        =                                          1                80                            ⁡                              [                                                      ∑                                          n                      -                      1                                        4                                    ⁢                                                            {                                                                        ∑                                                      x                            -                            1                                                    20                                                ⁢                                                                              (                                                          ld                              lt                                                        )                                                    x                                                                    }                                        n                                                  ]                                              ,                      
                    ⁢          and                ⁢                  xe2x80x83                ⁢                  
                                    Equation        ⁢                  xe2x80x83                ⁢        1                                          LY          =                                    1              K                        ⁢                                          ∑                                  y                  =                  1                                k                            ⁢              ly                                      ,                            Equation        ⁢                  xe2x80x83                ⁢        2            
wherein ld is the sum of length of the measurement straight lines across the worked faces, lt is the length of the straight, and ly is the width of the worked faces across one straight line having a length of 100 xcexcm in the measurement area, x indicates the measurement lines in the measurement area in each of the wire faces, n indicates 4 faces around the wire, and K indicates the number of the worked faces across one straight line.